Use cache for locality sort

lua/cmp/config/compare.lua

@@ -1,4 +1,5 @@
 local types = require('cmp.types')
+local cache = require('cmp.utils.cache')
 local misc = require('cmp.utils.misc')
 
 local compare = {}
@@ -102,6 +103,7 @@ end
 
 compare.locality = setmetatable({
   lines_count = 10,
+  lines_cache = cache.new(),
   locality_map = {},
   update = function(self)
     local config = require('cmp').get_config()
@@ -109,24 +111,36 @@ compare.locality = setmetatable({
       return
     end
 
-    self.locality_map = {}
-
     local win, buf = vim.api.nvim_get_current_win(), vim.api.nvim_get_current_buf()
     local cursor_row = vim.api.nvim_win_get_cursor(win)[1] - 1
     local max = vim.api.nvim_buf_line_count(buf)
+
+    if self.lines_cache:get('buf') ~= buf then
+      self.lines_cache:clear()
+      self.lines_cache:set('buf', buf)
+    end
+
+    self.locality_map = {}
     for i = math.max(0, cursor_row - self.lines_count), math.min(max, cursor_row + self.lines_count) do
       local buffer = vim.api.nvim_buf_get_lines(buf, i, i + 1, false)[1] or ''
+      local locality_map = self.lines_cache:ensure({ 'line', buffer }, function()
+        local locality_map = {}
         local regexp = vim.regex(config.completion.keyword_pattern)
-      while buffer ~= ''do
+        while buffer ~= '' do
           local s, e = regexp:match_str(buffer)
           if s and e then
             local w = string.sub(buffer, s + 1, e)
-          self.locality_map[w] = math.min(self.locality_map[w] or math.huge, math.abs(i - cursor_row))
+            locality_map[w] = math.min(locality_map[w] or math.huge, math.abs(i - cursor_row))
             buffer = string.sub(buffer, e + 1)
           else
             break
           end
         end
+        return locality_map
+      end)
+      for w, d in pairs(locality_map) do
+        self.locality_map[w] = math.min(self.locality_map[w] or d, math.abs(i - cursor_row))
+      end
     end
   end
 }, {